DEFORMATION, MELTING, AND RELAXATION OF STRUCTURED COLLOIDAL DISPERSIONS

Strongly interacting dispersions of spherical particles of silica and poly(vinylidene fluoride) have been prepared at high concentrations. The linear and nonlinear viscoelastic response of these systems have been investigated. These systems show a strong elastic response characteristic of viscoelastic ''solidlike'' behavior. It is demonstrated that by calculating the dimensionless internal energy density, a phase diagram can be constructed for the onset of viscoelastic solidlike behavior. The linear viscoelastic response has been calculated using a model for the relaxation spectrum which gives excellent agreement with the data. A model is proposed for the nonlinear viscoelastic response for small to moderate strains. It is based on the idea that increasing strain causes progressive melting of the order in the dispersion into a metastable liquid phase. It is demonstrated that when a scaled strain or an equivalent temperature is plotted against the fraction of liquid present, the nonlinear viscoelastic response of these systems can be reduced onto a master curve.